1. Field of the Invention
The present invention relates to an improved compact electromagnetic relay and, more particularly, to an electromagnetic relay which has a coil bobbin capable of increasing the number of turns of a coil without increasing an outer diameter of the coil and can be made compact.
2. Description of the Related Art
Recently, various electric and electronic parts are made compact, and a demand has arisen for a more compact electromagnetic relay accordingly.
However, a conventional compact electromagnetic relay has a structure similar to that of a comparatively large electromagnetic relay. Therefore, compactness of the conventional electromagnetic relay is limited, and its structure is complex to be manufactured.
FIG. 1 shows a structure of a main part of a conventional compact electromagnetic relay. In FIG. 1, reference numeral 1 denotes a coil bobbin. Guide hole 2 and through hole 3 are formed in bobbin 1, and coil 4 is wound around the outer surface of bobbin 1. One leg of each of a pair of U-shaped yokes 5 and 6 is inserted in guide hole 2, and armature 10 is inserted in through hole 3. One end portion of armature 10 is mounted on yoke 5 through hinge spring 9 which also serves as a hinge. When a current is flowed through coil 4, armature 10 is attracted to yoke 6 against a biasing force of spring 9. Reference numeral 13 denotes a contact block. Break contacts 19, 20 movable contacts 16 and 17, make contacts (not shown), and the like are integrally mounted on block 13. Drive card 22 is mounted on distal end portion 10a of armature 10. When armature 10 moves, card 22 presses movable contacts 16 and 17. Then, movable contacts 16 and 17 moved away from the break contacts 19, 20 and are brought into contact with make contacts 19.
The above structure of the conventional relay has the following various drawbacks in making the relay compact. First, compactness of bobbin 1 and coil 4 is limited. That is, the diameters of guide hole 2 and through hole 3 formed at the center of bobbin 1 must correspond to a total sum of the thicknesses of the legs of yokes 5 and 6 and armature 10 and a moving stroke of armature 10 and cannot be smaller than that. In addition, a magnet wire must be wound around coil 4 in a necessary number of turns. For these reasons, compactness of bobbin 1 and coil 4 is limited.
Furthermore, when the above electromagnetic relay is made compact, the moving stroke of the armature is reduced, and the contacts are also made compact. Therefore, the armature must be accurately moved. For this purpose, when the hinge spring is to be welded to the armature and the yoke, a positional relationship between these parts must be accurately regulated. However, it is difficult to accurately position and weld the above parts especially when, e.g., the hinge spring is small. In order to eliminate this drawback, one end portion of the armature is pivotally fitted in an end portion of the yoke, one end portion of the hinge spring is welded to the yoke or the like, and the other end portion of the hinge spring is mechanically fitted in the end portion of the armature. In this structure, the armature is tensioned to the yoke by a biasing force of the hinge spring so that the two parts are not removed from each other. However, in this structure, a play can be easily generated when the armature moves, and precision obtained upon movement is limited.
When such an electromagnetic relay is made compact, intervals between a plurality of movable contact springs are reduced accordingly, and therefore insulation breakdown easily occurs between the contacts. As a result, compactness of the electromagnetic relay is limited in this point of view.
The present invention has been made in consideration of the above situation and has as its object to provide an electromagnetic relay which is made compact, simple in structure, and can be easily manufactured.